The general objective of this proposal is to elucidate the mechanisms by which the interaction of actin and myosin underlying contraction of vascular smooth muscle is regulated in normal and hypertensive blood vessels. This proposal is based upon the hypothesis that the degree of phosphorylation of myosin directly controls force development in vascular smooth muscle. In order to investigate this hypothesis, the following studies are proposed: 1) investigation of the factors which control the degree of phosphorylation of mysoin light chains; 2) determination of the morphological and ultra-structural organization and coupling of contractile filaments and individual cells; and 3) determination of the relationship between the mechanical properties of whole muscle (force-veolocity-length) and the mechanical properties of the contractile apparatus. Strips of arterial smooth muscle stretched to Lmax will be activated by potassium de-polarization and frozen in liquid nitrogen. The myosin light chains will be separated and the degree of phosphorylation determined. The time course and magnitude of phosphorylation and isometric force development will be compared at different degrees of activation, i.e., (K ion)o. Detailed studies will be made on the control of actin-activated myosin ATP-ase activity, and of the degree of myosin phosphorylation by kinase and phosphatase enzyme systems. Pressure-fixed arterial segments will be used for detailed studies of vascular smooth muscle morphology using light and electron microscopy. These will include the organization of contractile filaments in the cell, intercellular coupling, and the arrangement of cells with respect to the vessel lumen. Intact segments will be used to determine the relation between muscle and contractile system mechanical properties. These segments will be subjected to pseudorandom length viscoelastic model representing vascular smooth muscle's mechanical properties.